1. Field of the Invention (Technical Field)
The present invention relates to apparatuses and methods for electroplating and electroforming, particularly by centrifugal means and for encapsulation, coating, and electrodeposition of powders, including into bands of mesh or film. The term "electrodeposition" as used throughout the specification and claims means electroplating and/or electroforming.
2. Background Art
The process for microencapsulation of metal hydride electrode powder (and other powders) has previously been limited to chemical copper and electroless nickel deposition. Previous studies of electroplating on fine particles employed equipment capable of handling the light material in an aqueous solution (see FIGS. 1 and 2) but the results were limited because of the difficulty of getting good electrical contact during circulation of the particles, poor cathode efficiency (loss to cathode contact plate and rise in solution ion concentration) and bipolarization, resulting in a costly and unreliable electrolytic process. Likewise, the alternative chemical copper or electroless nickel process was economically infeasible due to the high surface areas of powders.
Referring to FIG. 1 (prior art), a first known particle plating apparatus 11 consists of plating solution 12 surrounding particles 13, anode (Ni or Cu) 14, cathode 15, filter 16, propeller 17, storage tank 18, pump 19, Luggin's capillary 20, and Calomel electrode 21. A second known particle plating apparatus 31, shown in FIG. 2 (prior art), consists of plating bath 32 surrounding particles 33, anode 34, cathode 35, rotary axis 36, carbon brush 37, storage tank 38, pump 39, and tilting angle 40. As noted, these apparatuses are expensive and inefficient.
However, the benefits of microencapsulated metal hydride electrodes, Ishikawa et al, J. Less Common Met. 120:123 (1986), was an important enhancement to the performance and life of metal hydride (MH) batteries, which have twice the energy and life of NiCd cells. This encapsulation had two functions: to encapsulate the Misch metal (Mm) particle to prevent premature decomposition during usage while allowing flow through of gas, and to provide increased conductivity. Sakai et al, J. Less Common Met. 172-174:1194 (1991). This requires that the encapsulations be porous and have a stable interface. The difficulty of developing a cost effective process for making the encapsulation was a limiting factor for commercial applications, as was the need to subsequently compact or cold sinter the loose powder into a self-supporting flexible mesh or plug. The present invention provides such a cost effective process and apparatus for executing the microencapsulation process. The present invention also provides an apparatus and method for centrifugal electroforming of composite powders into mesh and films, which has not heretofore been possible.